High compression engine and pinging
 

Hey,

I just put in my '67 C10 a small block 350, with a non-stock cam and small chambered 283 heads on it. According to my cousin (which this engine is his), it has an 11.2:1 compression ratio. Last night, we got it in and started, and today I drove it around with 87 fuel. It runs smooth and strong and accelerates fine, but if I push a little more on the throttle it starts pinging. Any more pedal and it would start pinging and knocking worse (BTW this is with a 600cfm Edelbrock performer carb). I played around with the timing and it seems to run decent on 17 advanced for now. I plan to experiment with higher octane fuel, and:

I'd love your input on how I should go about with using higher octanes for this experimental engine. I don't know what to do to get rid of the pinging in this higher compression motor. I appreciate your help!

Tidbits:
I'm in CA, so all I can get is 91 (as far as I know). I do not know about octane boosters. There's a local airport where I could possibly try aircraft fuel.

Re: High compression engine and pinging
 

aircraft/race fuel would be best but very pricey.....this motor maybe a bit over built for street use I would consider putting in thicker head gaskets to drop the compretion as much as I could...9.5:1 is as much as most can stand on 93 octane without pulling a bunch of timing out of them maybe down as low as 8 to12*(OH boy I'm gonna get flamed for that) being old school and been though this I have used trany fluid to slow the burn down (ouch I'm going to get it again)

Alot is going to depend on what your going to use the truck for???

Re: High compression engine and pinging
 

I think you have the wrong Heads for the engine. 283 Heads have tiny 1.72" Intake valves & chambers. Larger chamber & valve needed.

Re: High compression engine and pinging
 

dream on with 87octane:lol:

Re: High compression engine and pinging
 

17 degrees static is far too much initial advance. I'd start by setting the timing per the sticky.

But....it ain't gonna run on 87 octane at 11.2. It's going to take premium fuel with a splash of some sort of octane increaser - avgas, racing gas or an aftermarket booster.

Re: High compression engine and pinging
 

I'll try even lower timing for the heck of it. I have heard from another source that a few ounces of tranny fluid in the tank does work. I'll try that too.
This is my only vehicle and daily driver. My (stock) 350 got busted from an oil leak while driving, and this engine was the closest solution to getting my truck on the road again.

Re: High compression engine and pinging
 

OK, I'll try less advance. Sorry, what do you mean setting per the sticky?

Yes, I was thinking before I'd try premium with a booster. Will do.

Re: High compression engine and pinging
 

I wouldn't; it's not going to increase the octane although it may slow the rate of combustion. One thing for sure - it's a solvent and it's going to raise all kinds of Hell with the carb.

Another option, not a great one - but workable - would be to go with a really thick head gasket. Going from an .028 to like an .056 or .060 would drop the CR into the 10.5 or so range which is a heckuva lot more reasonable and will probably run with full ignition advance on premium fuel...barely.

You end with with a horrifying quench, but this is all about making what you have work...

Re: High compression engine and pinging
 

See this post; long-winded but pretty good and although it looks a little intimidating it's not all that hard to do - and well worth a couple hours investment.

http://67-72chevytrucks.com/vboard/s...d.php?t=290498

Re: High compression engine and pinging
 

Do you know anything about the engine that you just stuck these random heads onto? cam part #?

What is the casting number from the cylinder heads? How was it determined that they are small chambered 283 heads?

Re: High compression engine and pinging
 

11.2-1 with iron heads is gonna to beat the pistons apart from all the pinging. DO NOT just go out and drive it even though its pinging. You will be sweeping the engine up when the internals exit via the window they make in the oil pan. Your best bet is to find something else to drive daily. You need over 100 octane to safely run that engine if it does indeed have 11.2-1 comp.Tickers suggestion will work also but if you pull those heads off to change gaskets you might as well just swap them for something with a more reason combustion chamber size.

Re: High compression engine and pinging
 

I would go with the timing suggestions as well. The cam can play a lot into it as well. A slightly big (I know that is a bit ambiguous) cam can actually help as it will bleed off compression at lower RPMs, but that might not be a first fix.

11.2 is a tad high but not totally unreasonable, except for maybe those heads. even vettes nowadays run 11:1 and don't have to have 90+ octane fuel. My dad ran a 10.25:1 BBC for 17 years with only 87 octane and drove it all over the country.

Re: High compression engine and pinging
 

there is no comparison between modern combustion chamber shapes in aluminum heads and the old tech of the 60's heads. You also have to keep in mind these are computer controlled engines with everything being monitored and adjusted constantly.

Re: High compression engine and pinging
 

retard the timing 4 to 8 degs

Re: High compression engine and pinging
 

:agree: Totally different situation.

Re: High compression engine and pinging
 

Yep... :agree:

Gary

Re: High compression engine and pinging
 

Just a thought...have you checked total timing? Could it be that you have too much mechanical and vacuum advance? Adjustable vacuum canisters are cheap, you can dial it back and get the total timing correct. I agree with the others, bring your initial back to about 12 degrees and see what happens. I run about 10.5:1 in my 350 and don't have detonation but then I make sure the total timing is in range too.

Re: High compression engine and pinging
 

Thanks for all your replies. I have yet to consider what everyone said, but I have an update: I filled up with 91 gas and used a Lucas 3x octane booster. After that I retarded the timing to 13 advanced. It runs much better now, with pinging only if I open the secondary barrels on the carb. I'll keep experimenting.

Re: High compression engine and pinging
 

Cool - but my only suggestion is stop experimenting until you get the timing set right as I noted previously.

It's not just about the initial timing but the total timing including advance, which from your description is where the issue is.

Re: High compression engine and pinging
 

Static & Dynamic compression are two different things. Have the cam specs?

Re: High compression engine and pinging
 

On an engine of this type, putting in a "too big" cam to bleed off DCR just ends up with a generally crappy-running engine that doesn't detonate.

DCR is a useful concept - on an engine making > 1.4 HP/CID or so.

Re: High compression engine and pinging
 

If you get the total timing set and it still knocks try a cooler plug. If I'm not mistaken that's a .375 reach gasket type plug on 283 heads. A Champion RJ12YC should be in the ballpark.

Re: High compression engine and pinging
 

Bottom line is that for a couple hundred bucks you can do a head swap if you shop around and use stock parts. People are practically giving away old casting 350 heads. A quick valve job and resurface and 50 bucks in gaskets and your back on the road without risk of melting or shattering a piston. Your going to probably end up detuned to the point the engine will run like sh!t and not even be worth bothering to go wide open throttle anymore to finally get the pinging to stop with the heads you have currently

Re: High compression engine and pinging
 

What about running a cam with a lot of overlap? I'm running 12:1 compression on 882 heads plus a 292 cam and I run it every day (its my daily driver) and still able to run on 93 (even on 87 it runs fine). This way it lowers your dynamic compression thus allowing you to run pump gas, but I'm no engine builder by any means so anybody please chime in if i'm wrong.:lol:

Re: High compression engine and pinging
 

As previously noted, a cam with a lot of overlap on an engine making less than about 1.4 HP/CID just wastes power, gas and driveability. Your engine would make significantly more power (on the order of 10-15% or more) with a lower static CR and the RIGHT cam. And it would make far more power where it spends most of it's time - below 4500 RPM.

This isn't intended to be harsh, but using DCR to run a high static CR is just bad engine design on a low-power, low-RPM engine. It's a crutch to make a bad combo work - but it doesn't work well. 1 point of CR is worth maybe 1.5 - 3% MAX on an engine making less than 1.4 HP/CID or so...so shooting for high CR for a street engine *does not* make power. It's a design technique for high-powered racing engines that has made it's way into street design.

Re: High compression engine and pinging
 

It sounds like a weekend project. I'll see if I can get to it. Hopefully it'll make a positive difference.

Re: High compression engine and pinging
 

Don't know about the cam (I didn't put it together) but the head # is 3795896 or
3884520 determined by the single triangle symbol, per this guide:
http://www.chevellestuff.com/qd/head...ng_by_year.htm

Only word I got on the cam right now is that it isn't stock.

Re: High compression engine and pinging
 

Yeah, well I guess the experiment with this engine is how efficient and lean it can run, so I guess my cousin's idea with putting these heads on was to see if the higher compression (and small intake) would equal +MPG.
I think the heads are great so far, 'cause I got this thing on the freeway and it accelerates more than my old (stock) 350 with powerpack heads.

Re: High compression engine and pinging
 

I agree, I definitely need to time my engine more accurately. I just haven't had time yet (school). I'll try to get to it this weekend.

Re: High compression engine and pinging
 

Thank you ticker for your previous link. Yes, I'll try to get to that this weekend.

Re: High compression engine and pinging
 

I have new AC Delco plugs in the engine. My cousin set the gap but he kept it modest.

Re: High compression engine and pinging
 

I agree, a big cam is NOT good for engines seeing low rpms, but a big cam will make more power, it just happens at a higher rpm due to overlap helping cylinder scavenging thus increasing volumetric efficiency. Also on engines, shouldnt you always shoot for the highest compression ratio possible (without detonation) since it results in higher efficiency thus leading to more power? Any time you raise compression you should always see a power gain (in theory), even if its a little bit. I wouldnt call it a bad combo, just probably not for a PURE street engine.

Re: High compression engine and pinging
 

i agree that running a larger cam to reduce DCR isn't a great idea, just that it can work. a real street engine that never/rarely sees the track will be far better off with the right cam and compression.

I also agree that a higher compression ratio will generally mean more power, assuming the cam is up to the task as well as the fuel. Race engines use high compression to make more power, but they also have the fuel to compensate.

Re: High compression engine and pinging
 

A big cam isn't going to make more power unless the heads can flow to the level of that lift. As an example, a big cam with 882 heads even if they're ported to a crazy extent isn't going to make power at high RPM...it just can't flow enough to use what the cam offers. And overall - a big cam making power at a crazy RPM level doesn't really do any good unless the car is regularly at that RPM level.

Compression ratio does improve volumetric and combustion efficiency...but again, only if the engine can make use of it. The more flow the engine can consume, then the more important CR becomes. Premium pump gas limits CR to around 10.2 with full ignition advance and an .040 quench....that's just as far as we can go on the toilet water we have for gas today. Going higher than that means giving up power - backing off on ignition advance or the previously mentioned DCR. For an engine running on pump gas, that 10.2 or so is the Golden Rule for a GEN I. We can push that a fair bit on a GEN II or LS due to the dramatically better combustion chamber shape, and even a bit with top-notch heads on a GEN I...but the gains are minimal unless it's a very hot engine. Vizard has an interesting chart that shows the benefits based on HP/CID - I'll see if I can scan and post it.

I would call the OP's engine a really bad combo. It can be made to work, but it's never going to work particularly well. The only thing we can do is figure out the crutches it's going to take to make it work without coming apart, and there have been a lot of good suggestions around that...but if budget is not an object, swapping the heads to get the CR into a reasonable place is the best choice.

Again, not trying to be :sumo: but this is the way it is :(

Re: High compression engine and pinging
 

Thanks for everyone's replies and advice. I simply don't have time to work on my truck 'cause of school, so I have my timing set to as advanced it will get without pinging, 15. It's a quick and dirty solution for now, but I still plan to take everyone's advice when I get the chance.
Thanks again and good trucking!